Quasi-adaptive method for determining a battery's state of charge

Abstract

A method and apparatus for determining the state of charge of a battery including determining a current-based state of charge measurement based on coulomb integration, determining a voltage-based state of charge measurement based on the resistance of said battery and a hysteresis voltage, and combining the current-based state of charge measurement and the voltage-based state of charge measurement to generate the state of charge measurement of the battery.

What is claimed is:  
     
       1. A method of determining the state of charge of a battery comprising: 
       determining a current-based state of charge measurement based on coulomb integration;  
       determining a voltage-based state of charge measurement based on the resistance of the battery and a hysteresis voltage; and  
       combining the current-based state of charge measurement and the voltage-based state of charge measurement with a weighting factor to generate the state of charge of the battery.  
     
     
       2. The method of  claim 1  wherein the step of determining the current-based state of charge is based on the equation:            SOC   C          (   t   )       =       SOC        (     t   -     Δ                 t       )       -       [       100                     [       (         η   I          I     t   -   1         +       η   I          I   t         )     /   2     ]       A                   h   nominal           +       (     S   D     )       t   -     Δ                 t           ]              Δ                 t     3600     .                         
     
     
       3. The method of  claim 1  wherein the step of determining a voltage-based state of charge further comprises determining the battery voltage using the open circuit voltage of the battery and the ohmic drop of the battery. 
     
     
       4. The method of  claim 3  wherein the step of determining a voltage-based state of charge further comprises determining the open circuit voltage of the battery as a function of temperature, hysteresis voltage and an initial state of charge of the battery. 
     
     
       5. The method of  claim 1  wherein the battery is a nickel/metal hydride battery. 
     
     
       6. A method of determining the state of charge of a nickel/metal hydride battery comprising: 
       determining a first state of charge measurement based on coulomb integration;  
       determining a second state of charge measurement based on a voltage model;  
       determining a weighting factor to be used in combining said first state of charge measurement and said second stage of charge measurement; and  
       combining said first state of charge measurement and said second stage of charge measurement to determine the state of charge of the nickel/metal hydride battery.  
     
     
       7. The method of  claim 6  wherein the step of determining the second state of charge measurement comprises: 
       determining the standard cell potential of the nickel/metal hydride battery;  
       determining the entropy of the cell reaction of the nickel/metal hydride battery; and  
       determining a hysteresis voltage of the nickel/metal hydride battery.  
     
     
       8. The method of  claim 6  further wherein the step of combining said first state of charge measurement and said second stage of charge measurement to determine the state of charge of the nickel/metal hydride battery comprises using the equation: 
       
         
             SOC=w ( SOC   C )+(1− w )( SOC   N ).  
         
       
     
     
       9. The method of  claim 6  wherein the step of determining the hysteresis voltage comprises monitoring the voltage and current of the battery. 
     
     
       10. A vehicle powertrain control system comprising: 
       a battery pack;  
       a power inverter coupled to said battery pack;  
       a controller controlling said power inverter, said controller monitoring the state of charge of said battery pack; and  
       a state of charge algorithm included in said controller, said state of charge algorithm based on a coulomb integration method and a voltage based model.  
     
     
       11. The vehicle powertrain control system of  claim 10  wherein said battery pack comprises at least one nickel/metal hydride battery. 
     
     
       12. The vehicle powertrain control system of  claim 10  wherein said battery pack comprises a plurality of nickel/metal hydride batteries connected in series. 
     
     
       13. The vehicle powertrain control system of  claim 10  wherein said battery pack comprises at least one lead acid battery. 
     
     
       14. The vehicle powertrain control system of  claim 10  wherein said battery pack comprises at least one lithium battery. 
     
     
       15. The vehicle powertrain control system of  claim 10  wherein said controller is capable of communicating over an automotive communications network. 
     
     
       16. The vehicle powertrain control system of  claim 15  wherein said automotive communications network comprises a CAN network. 
     
     
       17. The vehicle powertrain control system of  claim 10  further comprising a motor/generator coupled to said inverter.